1. Field of the Invention
The present invention relates to a free electron laser with an improved electron accelerator. It is used in the production of coherent radiation in a range extending from the submillimetre to the near infrared.
2. Discussion of the Background
A prior art free electron laser is diagrammatically shown in FIG. 1. It comprises an electron source K producing an electron beam, an accelerating structure ACC accelerating said beam to relativistic velocities, deviators DEV1, DEV2, making it possible to introduce the accelerated beam into a magnetic structure which is called a wiggler and which is formed from periodically alternating magnets. The electron beam undergoes a series of deflections in alternating directions within said wiggler. At the output, the electron beam is again deflected by a deviator DEV3 and is finally absorbed by an attenuator A. The wiggler is surrounded by two mirrors M1 and M2.
In the represented variant, an oscillator OSC supplies an electromagnetic beam L1, which passes through the wiggler. The latter is the seat of an interaction between the electron beam and the electromagnetic beam. If certain conditions are respected, the electromagnetic beam is amplified at the expense of the energy of the electron beam. An intense, coherent laser beam L2 is emitted and directed towards the use means.
A free electron structure can also function as an oscillator. In this case, the mirrors M1 and M2 are parallel and form a resonant cavity. The oscillator OSC is naturally absent in this case.
Hereinafter the word "laser" is consequently understood to mean both an amplifier and an oscillator.
A description of this device appears in U.S. Pat. No. 3,882,410.
The optimization of the operation of a free electron laser is partly based on the parameters of the electron beam injected into the wiggler. Among these parameters are the intensity of the beam, the energy of the electrons, the dispersion of the velocities and the diameter of the beam.
In the hitherto known electron lasers, various accelerating structures are used, such as:
linear accelerators for energies between 20 and 120 MeV, PA0 linear induction accelerators from 0.5 to 5 MeV, PA0 electrostatic accelerators (of the Van de Graaff type) from 3 to 6 MeV, PA0 diode supplied by a Marx generator from 0.15 to 1 MeV, PA0 storage rings from 150 to 540 MeV, PA0 microtrons from 100 to 150 MeV.
For example, in GB-A-2 065 363 use is made of a linear accelerator (or linac/catalac), whilst a microtron is used in the article "Proposal for FEL Experiments Driven by the National Bureau of Standard's CW Microtron".
Although accelerators are suitable from certain aspects, they still suffer from disadvantages. In particular, their complexity is such that it is difficult to produce an industrial laser, i.e. having reduced overall dimensions, a low cost and a good reliability. Moreover, the energy efficiency of conventional accelerators is not very high, whilst the energy dispersion of the accelerated electrons is excessive. Thus, the free electron laser has hitherto remained a laboratory tool.
Moreover, the accelerators used in the last two documents referred to hereinbefore suffer from the problem of switching of the electron beam. Thus, in these devices, the electron beam follows a common trajectory portion in the accelerator (no matter whether it is a linac or microtron) and must cover different trajectories on the outside. This makes it necessary for mixing and separating devices for the electron beams.